Time-limit fuse



B. M. MOUERS AND L. E. WARNER.v TIME LIMIT FUSE. APPLICATION FILED A'uGJa. 1917.

1,361,396,V I v Patented Dec.l 7, 1920.

M@ am @mf A TTOHNEYS BENJAMIN M. MOOERS, OF SAN FRANCISCO. AND

PATENT OFFICE.

LAWRENCE E. WARNER, OF BERKE- LEY, CALIFORNIA, ASSIGrNOLRS T0 MOTOR PROTECTOR MANUFACTURING COMPANY, 0F SAN FRANCISCO, CALIFORNIA, A CORPORATION OF CALIFORNIA.

TIME-LIMIT FUSE.

To all whom z't'mag/ conce/lm:

Be 1t known that we, BENJAMJN M.

1 u. Moonns and LAWRENCE It. VARNER, citizens of the United States, and residents, respectively, of the city and county of San Francisco and of Berkeley, county of Alameda,

jected to the heat generated by theflow of,

current in a. heating' coil 'surrounding'or otherwise arranged adjacent to the fuse.

An object of the invention is to provide a fuse of the type described in which means are4 provided for preventing the molten material of the fuse from keeping the circuit closed, after the fuse has melted.

The invention possesses other advantageous features, some of which, with the foregoing, will be set forth at length in the following description, where we shall outline in full, that specific form of the invention which-we have selected for illustration in the drawings accompanying and forming part of the present specification,

Referring to saiddrawings:

Figure l is a longitudinal sec-tion of one form of fuse of our invention.

Fig. 2 is a longitudinal section of the fuse of our invention inc losed in a molded fuse casing.

Fig. 3 is a cross section of the fuse shown .in Fig. 2.

In fuses of this type, the fuse element or wire is arranged in series with the heating coil. which usually surrounds the fuse.

'iVith these conditions of construction, the molten fuse metal freouently closes the circuit between the coil and the fuse at some point other than its original point of ccnnection, so that the circuit is not opened by the melting of the fusible metal. Further, when the fuse unit is so disposed that -the fusible element and the surrounding heating coil are disposed in a horizontal plane,

the molten metal lies Within the core of the Specification of Letters Patent.

Patented Dec.' 7, 1920.

l Application led August 13, 1917. Serial No. 185,883.

coil frequently continuing the circuit. Since it is desirable to open the circuit immediately when such conditions obtain as to melt the fuse, the conditions set forth above present serious disadvantages.

It is an object, therefore, of our invention to overcome these disadvantages and we accomplish this result by providing within the fuse unit a chamber or casing into which the moltenv metal fiows, and in which it is out of contact with the heating coi-l and the still solid portions of the fuse wire. u

A further feature of our invention is the heat lagging of the heating coil. so that, with acurrent flowing and thefuse unit in circuit with electrical apparatus, the tem-A perature of the heating coil corresponds directly with the temperature of a selected portion of the apparatus being protected and preferably thehottest portion of such apparatus. This is accomplishedby surrounding the heating coil with a shellI of heat-insulating material of such propor tions, that the heating coil yhas the same heat emissivity as that part of the electrical apparatus being protected in which the highesty deleterious temperature obtains.

The fuse unit of our invention comprises a fusible element 2, preferably in the form of a rod or wire. Surrounding` and inclosing a portion of the fusible element in the construction shown in rig. l, is a cup 3, preferably formed of porcelain or other insulating material, and the cup is preferably formed of two parts fitted together. Connected to one end of the fusible element is one end of a heating coil which is wound around the fusible element in two sections or coils 4.-5, one lying on.each side of and adjacent the cup. When the fusible metal is melted by a suflicient increase in temperature the molten -metal flows into the chamber within the cup, Where it is contact with the heating coil and the re mainingir unmelted partsof the fusible element. The fusible element is of such size that it will not melt under the heating effect of van overload current therethrough until the heating eifect of the overload current in the apparatus produces a temperan ture therein which approaches the danger point. For example, in protecting an electric motor which takes a S35-ampere starting .end caps lll-15.

`chamber and current and an 83ampere normal load current, a 25-ampere fusible element is employed, which fusible element will carry the starting current during the time necessary for starting the motor.

The fusible element and the heating coil are inclosed in a heat-insulating casing 6, havin metallic ends or caps 7 to which one end o? fusible element are connected and the casing is filled With a packing 8 of asbestos or similar material.

Instead of constructing the fuse unit of a casing with its filling and cup, the fuse casing may be molded of porcelain, bakelite or other comparable material, into the desired form, to produce a chamber therein into which the molten metal may flow. In this construction, the fuse casing is formed in two parts 12 and 13 which are Vfitted together and held to ether preferably by the he casing is molded to form a chamber 16 through which the fusible element 2 extends, and contiguous charnbers 17 and 18 onopposite sides thereof, in which the heating coils 41-5 are disposed. The central chamber 16 is preferably larger than the contiguous chambers so that the molten metal deposited therein will not contact With the heating coils and the unmelted part of the fusible element.

e claim:

1. A protective device for electric circuit, comprising a casing having a chamber therein, a fusible element extending through said chamber land projecting from opposite sides of the chamber,and heating coils surrounding the projecting portions of the fusible element. r

2. A protective device for electric circuit,

comprising a casing having a chamber therein, a fusible element extending through said projecting from opposite sides of the chamber, and a heating coil in series with the fusible element and formed in two sections each section surrounding a projecting portion of the fusible element.

the heating coil and one end of the 3. A protective device for electric circuit, comprising a-fusible element, a cup of insulating material surrounding a portion of said fusible element so that the element projects from opposite sides of the cup, and a heating coil formed in two sections and surrounding the projecting portions of the fusible element.

. 4. A protective device for electric circuit, comprising a casing having a chamber therein, contacts arranged at the ends of the casing, a fusible element connected to one of said contacts and extending through said chamber and projecting from opposite sides thereof and heating coils connected to said element and the other contact arranged in series and surrounding projecting portions of said element.

5. A protective device for electric circuit, comprising a cylindrical casing having a chamber therein, a fusible element disposed Iaxially of the casing in said chamber. heating coils connected in series with said eleand to the other contact arranged within said casing on opposite sides axially of said chamber and heat insulating material surrounding said coils.

In testimony whereof, We have hereunto set our hands at San Francisco, California, this 27th day of July, 1917.

BENJAMIN M. MOOERS. LAVRENCE E. WARNER.

In presence of- H.'G. PRos'r. 

